System for amplifying an optical pulse using a diode-pumped, Q-switched, intracavity-doubled laser to pump an optical amplifier

ABSTRACT

An efficient, powerful and reliable system for amplifying optical pulses. Seed-pulses are generated by a seed-pulse source and are transmitted to an optical amplifier for amplification. The power for the amplification is provided by a Q-switched, diode-pumped, intracavity-doubled pump laser.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of lasers, and moreparticularly to lasers for pumping optical amplifiers.

2. Description of the Background Art

Known amplifier systems employ a source laser, an amplifier, and a pumpsource to transfer energy to the amplifying medium, to generateamplified laser light. The source laser emits a beam of laser light thatis amplified as it passes through the amplifier. The energy for theamplification is provided to the amplifier by the pump source, which istypically a laser. A pump laser generally includes a laser mediumelement, positioned between a high reflector and an output coupler, anda pumping means. The pumping means excites the atoms of the mediumelement into a metastable state. The relaxation of the excited atoms isaccompanied by the emission of light, which is reflected back and fourthbetween the high reflector and the output coupler, and the growingreflected wave induces the emission of additional light into thereflected wave state. As the wave continues to grow, the output couplerallows a portion of the reflected light to pass as the output beam ofthe pump laser.

It is obviously desirable that the pump laser be efficient, powerful,reliable, and convenient to set up and operate, but often there istension between these various design objectives. For example, diodelasers provide a very efficient pumping means and are more durable thanlamps, but the output energy of known diode-pumped lasers has been toolow for them to function effectively as amplifier pumping lasers.Further, some prior diode-pumped systems require that the pitch of thediode emitters be carefully matched and aligned to the optical pathwithin the media element, reducing convenience of assembly.

More powerful pump lasers exist, but in each case the power increasecomes at the expense of one of the other design objectives. For example,more power can be obtained by using gas filled lamps to excite the pumplaser lasing medium, but these systems are less efficient, lessreliable, and less robust. Additionally, such lasers generally havesignificant cooling requirements and require a special power service, asopposed to a standard 110 V AC outlet.

Thus, there is a need for a laser amplifier system capable of producingan output that is orders of magnitude higher in energy than knowndiode-pumped systems. It is also desirable that the amplifier system beefficient, reliable, and convenient to set up and operate.

SUMMARY OF THE INVENTION

The present invention is an efficient, powerful and reliable opticalamplification system. Seed-pulses are generated by a seed-pulse sourceand are transferred to an optical amplifier for amplification. The powerfor the amplification is provided by a Q-switched, diode-pumped,intracavity-doubled amplifier pump laser.

One embodiment of the amplifier pump laser includes a laser mediumelement that is pumped by a plurality of diode lasers to emit a beam oflight at a first frequency along an optical path passing through theelement. The pump laser also includes at least one reflector and anoutput coupler, for redirecting the beam along the optical path toestablish an optical resonator. A Q-switch is disposed in the opticalpath to selectively frustrate or permit optical resonance, therebyenabling the laser to produce high-power output pulses, as opposed tolow-power, continuous output. The output power of the pump laser isfurther enhanced by including a doubling crystal within the opticalcavity. The doubling crystal is disposed in the optical path andconverts a portion of the original oscillating wave to a new wave havingtwice the frequency of the original. The output coupler is highlyreflective to the original frequency, but highly transmissive to thedoubled frequency, and, therefore, passes the doubled frequency wave asoutput.

There are several specific embodiments of the amplifier pump laser ofthe present invention. One embodiment is characterized by a beam that isdirected between two reflectors, along a folded optical path, by a beamdirector and an output coupler. Another embodiment is characterized by astraight optical path between one reflector and the output coupler.Finally, there are unidirectional and bi-directional ring configuredembodiments.

One embodiment of the optical amplifier of the present invention is aregenerative amplifier which includes a gain medium element within anoptically resonant cavity, a capturing means for switching seed-pulsesinto the cavity, and an ejecting means for switching amplified pulsesout of the cavity. The output beam of the amplifier pump laser excitesthe gain medium, which amplifies the seed-pulse as it oscillates withinthe cavity. After amplification, the ejecting means switches theamplified pulse out of the cavity as the amplification system output.

Other embodiments of the optical amplifier include a ring configuredregenerative amplifier and a multi-pass "bow-tie" amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the preferred optical amplification systemof the present invention;

FIG. 2 is a block diagram of the diode-pumped, Q-switched,intracavity-doubled pump laser of FIG. 1;

FIG. 3 shows an end view of the laser medium element of FIG. 2;

FIG. 4 is a block diagram of the optical amplifier of FIG. 1;

FIG. 5A is a block diagram of an alternate amplifier pump laser;

FIG. 5B is a block diagram of an alternative amplifier pump laser havinga bi-directional, ring configuration;

FIG. 5C is a block diagram of an alternative amplifier pump laser havinga uni-directional, ring configuration;

FIG. 6A is a block diagram of an alternate ring-configured opticalamplifier; and

FIG. 6B is a block diagram of an alternate multi-pass optical amplifier.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention provides an efficient, powerful, reliable, andconvenient optical amplification system. Numerous details, such as thenumber of diode lasers and the use of a regenerative amplifier, areprovided for the sake of clarity, but it will be obvious to thoseskilled in the art that the invention can be practiced apart from thesespecific details. In other instances, details of well known equipmentand processes are omitted so as not to obscure the invention.

FIG. 1 shows an optical amplification system 100, including a seed-pulsesource 110, an optical amplifier 112, and an amplifier pump laser 114.Seed-pulse source 110 generates seed-pulses and sends them via opticalpath 116 to optical amplifier 112. Amplifier pump laser 114 generatespump pulses which are directed along optical path 118 into amplifier112. Amplifier 112 uses the optical energy of the pump pulses to amplifythe seed-pulses and emits the amplified pulses along optical path 120.

Seed-pulse source 110 includes pump laser 122 and oscillator 124. Pumplaser 122 provides optical energy, via optical path 126, which excitesoscillator 124 to emit the seed-pulses along optical path 116. In thepreferred embodiment, pump laser 122 is a continuous-wave laser andoscillator 124 is a titanium-sapphire oscillator. Seed-pulse sources arewell known in the art, and therefore will not be discussed in greaterdetail.

FIG. 2 shows a detailed view of amplifier pump laser 114, including afirst reflector 202, a Q-switch 204, a laser medium element 206, aplurality of diode lasers 208, a second reflector 210, an output coupler212, a frequency altering device 214, and a third reflector 216. In thepreferred embodiment, laser medium element 206 is a cylindrical rod ofneodymium-doped yttrium-lithium-fluoride (YLF), but those skilled in theart will understand that the invention may be practiced with alternateactive elements, such as erbium (Er) holmium, (Ho) or thorium (Th), oralternate carriers such as glass, vanadate, oryttrium-scandium-gallium-garnet (YSGG). Diode lasers 208 are disposedalong the lateral surface of laser medium element 206, and when providedwith electrical current emit laser light into element 206 which excitesthe atoms of element 206 to a metastable state. The relaxation of theexcited atoms is accompanied by the emission of light of a firstfrequency (w), some of which travels along a folded optical path 218.

Reflectors 202 and 216 are positioned at opposite ends of optical path218, and each respectively has a reflective surface 220 and 222 which issubstantially perpendicular to an incident segment of optical path 218.Therefore, any light traveling along optical path 218 which is incidenton either reflector 202 or 216 is reflected back along optical path 218.Reflector 210 and output coupler 212 fold optical path 218 to passbetween reflectors 202 and 216, through Q-switch 204, laser mediumelement 206 and frequency altering device 214. As the light oscillatesback and forth between reflectors 202 and 216, the growing reflectedwave induces the emission of additional light into the reflected wavestate, thus amplifying the reflected wave.

Q-switch 204 is disposed in optical path 218 between reflector 202 andlaser medium element 206 and selectively frustrates or permitsoscillation. When oscillation is frustrated, the excited atoms are notinduced to emit light, and the number of excited atoms can, therefore,be greatly increased. Then, when Q-switch 204 permits oscillation, apowerful pulse will be generated as the large number of excited atomsdrop to the lower state, emitting light as they make the transition.Many Q-switching arrangements are known, including, but not limited to,bleachable absorbers that become transparent under illumination,rotating prisms and mirrors, mechanical choppers, ultrasonic cells, andelectro-optic shutters such as Kerr or Pockels cells. The presentinvention contemplates the use of any such switching device.

Frequency altering device 214 is disposed in optical path 218, betweenreflector 216 and output coupler 212. In the preferred embodiment,frequency altering device 214 is a lithium-triborate (LBO) doublingcrystal, but those skilled in the art will understand that the inventionmay be practiced with alternative doubling crystals, including but notlimited to beta-barium-borate (BBO), potassium-titanyl-phosphate (KTP)and potassium-dihydrogen-phosphate (KDP). As the light of frequency (w)emitted by laser medium element 206 travels along optical path 218through device 214, the frequency of a portion of the beam is doubled,creating a second wave at the doubled frequency (2w). Output coupler 212is designed to be highly reflective to the first frequency (w) buttransparent to the second (2w) frequency, and therefore passes thesecond (2w) wave as an output pulse along optical path 118. Theintracavity disposition of device 214 is advantageous over prior artsystems which positioned the doubling crystal between the amplifier pumplaser and the optical amplifier. Since the reflected (w) wave makesmultiple passes through device 214, the doubling efficiency is greatlyincreased, resulting in an increase in output power.

FIG. 3 shows an end view of laser medium element 206, taken alongoptical path 218. The plurality of diode lasers 208 are disposed alongthe circumference of medium element 206 which, except for openingsthrough which diode lasers 208 emit their light, is surrounded by ahighly reflective material 310. The reflective material 310 increasesefficiency by insuring that the light emitted by diode lasers 208 makesseveral passes through medium element 206, thus increasing theopportunity for absorption. Those skilled in the art will understandthat a suitable choice of neodymium concentration in the YLF or asuitable distribution of the pump diodes around the rod could eliminatethe need for the reflective material. Those skilled in the art will alsounderstand that the laser beams emitted by diode lasers 208 aretypically diverse, and are shown in FIG. 2 as narrow rays for the sakeof clarity.

FIG. 4 is a block diagram detailing optical amplifier 112, whichincludes a gain medium element 402, first and second reflectors 404 and406, first and second Pockels cells 408 and 410, a polarizing beamsplitter 412, and first and second beam directors 414 and 416. In thepreferred embodiment, gain medium element 402 is a cylindrical rod oftitanium-doped sapphire (Ti:Al₂ O₃) having a first end surface 418 and asecond end surface 420, each formed by a Brewster cut. Reflectors 404and 406 each have a highly reflective surface 422 and 424 respectively,and are positioned facing each other at opposite ends of gain mediumelement 402 with their reflective surfaces 422 and 424 perpendicular toan optical path 426 passing through both end surfaces 418 and 420 ofgain medium element 402. First and second Pockels cells 408 and 410 aredisposed in optical path 426, between gain medium element 402 and firstand second reflectors 404 and 406, respectively. Polarizing beamsplitter 412 is disposed in optical path 426 between gain medium element402 and second Pockels cell 410.

During operation, seed-pulses emitted by seed-pulse source 110 alongoptical path 116 impinge on first end surface 418 of gain medium element402. Although the angle appears smaller in FIG. 4 for purposes ofillustration, optical path 116 forms an angle of about 114° with opticalpath 426. The reflected seed-pulse is polarized, and optical path 116 isoriented relative to gain element 402 such that the polarized seed-pulseis reflected along optical path 426 toward first Pockels cell 408. FirstPockels cell 408 selectively switches a seed-pulse into opticalamplifier 112, where the pulse is amplified during several passes alongoptical path 426 between reflectors 404 and 406.

The energy for the amplification that occurs in optical amplifier 112 isprovided by amplifier pump laser 114. First beam director 414 redirectsthe pump light emitted from amplifier pump laser 114 along optical path118 to impinge on first end surface 418 of gain medium element 402. Thepump light passes through first end surface 418 and is absorbed by theatoms of gain medium element 402, exciting them to a metastable state.The excited atoms are induced by the oscillating seed-pulse to re-emitthe absorbed light into the seed-pulse state, thereby amplifying theseed-pulse.

After a number of passes between first and second reflectors 404 and 406along optical path 426, second Pockels cell 410 ejects the amplifiedpulse by altering its polarization such that polarizing beam splitter412 directs the pulse toward second beam director 416, which in turndirects the pulse along optical path 120 out of optical amplifier 112.Those skilled in the art will understand that there are many opticalswitching techniques that can be used to switch pulses into and out ofthe regenerative amplifier resonator. These include a single Pockelscell, multiple Pockels cells, a combination of a Pockels cell and a waveplate, acousto-optic cells, Faraday isolators, and a multitude of othercombinations of the foregoing. The invention contemplates the use ofeach of these and other types of switching techniques, and is limitedonly by the appended claims.

While amplifier 112 of the preferred embodiment of the invention hasbeen disclosed as a linear regenerative amplifier, it will be obvious tothose skilled in the art that the invention may be practiced with othertypes of optical amplifiers. In fact, the invention contemplates the useof other types of amplifiers, and is limited only by the appendedclaims.

FIG. 5A is a block diagram of an alternate amplifier pump laser 114acharacterized by a straight-line optical path 502. Alternate pump laser114a includes a laser medium element 504, a plurality of diode lasers506, a reflector 508, an output coupler 510, a Q-switch 512, and afrequency altering device 514. Diode lasers 506 are disposed along thelateral surface of laser medium element 504, and when provided withelectrical current emit laser light into element 504 which excites theatoms of element 504 to a metastable state. The relaxation of theexcited atoms is accompanied by the emission of light of a firstfrequency (w), some of which travels along optical path 502.

Reflector 508 and output coupler 510 are positioned to face each otherat opposite ends of optical path 502. Reflector 508 and output coupler510 each have a reflective surface 516 and 518 respectively which issubstantially perpendicular to optical path 502. Therefore, any lighttraveling along optical path 502 which is incident on either reflector508 or output coupler 510 is reflected back along optical path 502. Asthe light oscillates back and forth between reflector 508 and outputcoupler 510, the growing reflected wave induces the emission ofadditional light into the reflected wave state, thus amplifying thereflected wave.

Q-switch 512 is disposed in optical path 502 between reflector 508 andlaser medium element 504 and selectively frustrates or permitsoscillation. When oscillation is frustrated, the excited atoms are notinduced to emit light, and the number of excited atoms can, therefore,be greatly increased. Then, when Q-switch 512 permits oscillation, apowerful pulse will be generated as the large number of excited atomsdrop to the lower state, emitting light as they make the transition.

Frequency altering device 514 is disposed in optical path 502, betweenlaser medium element 504 and output coupler 510. As the light offrequency (w) emitted by laser medium element 504 travels along opticalpath 502 through device 514, the frequency of a portion of the beam isdoubled, creating a second wave at the doubled frequency (2w). Outputcoupler 510 is designed to be highly reflective to the first frequency(w) but transparent to the second (2w) frequency, and therefore passesthe second (2w) wave as an output pulse along optical path 118.

FIG. 5B shows an alternate bi-directional, ring-configured amplifierpump laser 114b, which could be substituted for amplifier pump laser114. Pump laser 114b is characterized by a triangular optical path 520,and includes a laser medium element 524, a plurality of diode lasers526, a first beam director 528, a second beam director 530, an outputcoupler 532, a Q-switch 534, and a frequency altering device 536. Diodelasers 526 stimulate laser medium element 524 to emit light of a firstfrequency in both directions along optical path 520. As described above,Q-switch 534 pulses laser 114b, and frequency altering device 536doubles the frequency of a portion of the light passing therethrough.Beam directors 528 and 530 are disposed at two of the vertices ofoptical path 520 to direct light incident from one leg of optical path520 along the adjacent leg. Output coupler 532 is disposed at theremaining vertex of optical path 520 and is designed to reflect light ofthe first frequency and transmit light of the doubled frequency asoutput beams along optical paths 118 and 538.

It will be clear to one skilled in the art that optical path 520 neednot be triangular. With the addition of an appropriate number of beamdirectors optical path 520 could be shaped as any multi-sided polygon.Further, additional laser medium elements may be disposed in one or moreof the additional legs to create a more powerful multi-element laser.All such modifications are considered to be within the scope of thepresent invention.

The dual output is a result of the bi-directional operation of laser114b. Light traveling along optical path 520 in a clockwise directionwill be emitted along optical path 118, whereas light traveling alongoptical path 520 in a counter-clockwise direction will be emitted alongoptical path 538. Bi-directional operation is desirable when two outputbeams are required. When only one output beam is required, the secondbeam results in wasted power, and uni-directional operation ispreferred.

FIG. 5C shows an alternate unidirectional, ring-configured amplifierpump laser 114c, which could be substituted for amplifier pump laser114. Ring laser 114c is substantially identical to ring laser 114bdescribed above, but includes an additional uni-directional device(optical diode) 550. Typically, optical diodes include a Faradayrotator, an optically active crystal and a Brewster plate. Faradayrotators rotate the polarization of a beam in a direction of rotationthat is not dependent on the direction of travel of the wave, but thedirection of rotation by the optical crystal does depend on thedirection of travel of the wave. Therefore, in one direction the effectof the two components combine to produce a net rotation, but in theother direction they offset, producing no net rotation. The Brewsterplate then selectively introduces a loss in the direction undergoing anet rotation, frustrating oscillation in that direction. Other means forencouraging unidirectional oscillation are known to those skilled in theart, and are considered to be within the scope of the invention.

FIG. 6A shows an alternate ring-configured, regenerative opticalamplifier characterized by a rectangular optical path 602 and includingfour beam directors 604, 606, 608, and 610, a gain media element 612, aPockels cell 614 and a polarizing beam splitter 616. Beam directors 604,606, 608, and 610 are each disposed at one of the vertices of opticalpath 602, to redirect light incident from one leg of optical path 602along the adjacent leg. Gain element 612 has a first end surface 618 anda second end surface 620, and is disposed between beam directors 604 and610 such that optical path 602 passes through first and second endsurfaces 618 and 620 of gain element 612. Pockels cell 614 andpolarizing beam splitter 616 are disposed in optical path 602 betweenbeam directors 606 and 608, with beam splitting polarizer 616 nearerbeam director 606.

A polarized seed-pulse enters amplifier 600 via optical path 622, and isreflected along optical path 602 toward beam director 610 by the secondend surface 620 of gain element 612. The seed-pulse travelscounter-clockwise around optical path 602, first being reflected by beamdirectors 610 and 608, then passing through Pockels cell 614 whichalters its polarization and, thus, it passes through polarizing beamsplitter 616, then being reflected by beam directors 606 and 604, andfinally passing through gain element 612.

The seed-pulse is amplified as it repeats the loop around optical path602. The power for amplification is provided by a pump laser whoseoutput beam enters amplifier 600 via optical path 626. The pump beampasses through first end surface 618 of gain element 612 where it isabsorbed by the active atoms of the gain medium, exciting them to ametastable state. The oscillating seed-pulse induces the excited atomsto re-emit the absorbed light into the seed-pulse state, therebyamplifying the seed-pulse. After a number of amplifying passes aroundoptical path 602, Pockels cell 614 ejects the pulse by altering itspolarization such that polarizing beam splitter 616 directs the pulsealong optical path 624 out of optical amplifier 600. Those skilled inthe art will recognize that there many techniques, for example thosedescribed above, for switching a pulse into and out of a regenerativeamplifier, and the present invention contemplates the use of any suchswitching technique.

FIG. 6B shows an optional multi-pass optical amplifier 650,characterized by a "bow tie" shaped optical path 651, including a gainelement 652 and four beam directors 654, 656, 658, and 660. A seed-pulseenters amplifier 650 along optical path 662 and passes through gainelement 652 and proceeds along optical path 651 toward beam director654. Beam director 654 redirects the pulse along the next leg of opticalpath 651 toward beam director 656, which in turn redirects the pulseback through gain element 652 and toward beam director 658. Beamdirector 658 then directs the pulse toward beam director 660, which inturn directs the pulse through gain element 652 a third time and out ofamplifier 650 via optical path 664. The pulse is amplified each time itpasses through gain element 652, with power provided by a pump laserbeam.

Those skilled in the art will recognize that there are many variationson this type of amplifier. In its simplest form, an amplifier of thistype could consist simply of a gain element and a pumping means, withthe beam making only one pass (although this is not technically amulti-pass amplifier) through the element. At the other extreme, a largenumber of beam directors could be arranged around the gain element,greatly increasing the number of passes by the beam through the gainelement.

The present invention has been disclosed with reference to a preferredembodiment and several alternate embodiments. Specific details have beenset forth, such as the number of medium elements in a pump laser oramplifier, specific beam paths, and methods for switching pulses intoand out of an amplifier. Those skilled in the art will understand thatthe invention may be practiced apart from the specific details set forthherein.

We claim:
 1. A system for amplifying optical pulses comprising:aseed-pulse source for producing optical seed-pulses; an opticalamplifier disposed to receive said seed-pulses from said seed-pulsesource, for receiving and amplifying said seed pulses and for outputtingamplified seed-pulses; and a diode-pumped, amplifier pumping laser forproviding optical energy to said optical amplifier for the amplificationof said seed-pulses, said amplifier pumping laser including anintracavity frequency altering device and a switching means forselectively frustrating or allowing optical resonance, thereby enablingsaid amplifier pumping laser to emit pulses of laser light.
 2. Thesystem of claim 1 wherein said optical amplifier is a regenerativeamplifier.
 3. The system of claim 2 wherein said regenerative amplifieris a linear regenerative amplifier.
 4. The system of claim 3 whereinsaid amplifier pumping laser comprises:a laser medium element foremitting a laser beam at a first optical frequency along an optical pathpassing through said element; a diode laser for emitting laser light toexcite said laser medium element to emit said laser beam; a firstreflector disposed at a first end of said optical path for redirectingsaid beam back along said optical path; a frequency altering deviceinterposed in said optical path for altering the frequency of a portionof said beam from said first frequency to a second frequency; an outputcoupler disposed to reflect light of said first frequency along saidoptical path and to pass light of said second frequency as amplifierpump laser output pulses; and a switching device disposed in saidoptical path and responsive to an external signal, for selectivelyfrustrating or allowing optical resonance.
 5. The system of claim 4wherein said laser medium element is a cylindrical solid.
 6. The systemof claim 5 wherein said laser medium element includes neodymium.
 7. Thesystem of claim 6 wherein said laser medium element further includesYLF.
 8. The system of claim 7 wherein said diode laser is disposed toside pump said laser medium element.
 9. The system of claim 8 whereinsaid switching device is an acousto-optical cell.
 10. The system ofclaim 9 wherein said frequency altering device is an LBO crystal. 11.The system of claim 9 wherein said frequency altering device is a BBOcrystal.
 12. The system of claim 9 wherein said frequency alteringdevice is a KTF crystal.
 13. The system of claim 9 wherein saidfrequency altering device is a KDP crystal.
 14. The system of claim 8wherein said switching device is an electro-optical cell.
 15. The systemof claim 7 wherein said diode laser is disposed to end pump said lasermedium element.
 16. The system of claim 6 wherein said laser mediumelement further includes YAG.
 17. The system of claim 16 wherein saidswitching device is an acousto-optical cell.
 18. The system of claim 16wherein said switching device is an electro-optical cell.
 19. The systemof claim 6 wherein said laser medium element further includes YSGG. 20.The system of claim 6 wherein said laser medium element further includesvanadate.
 21. The system of claim 6 wherein said laser medium elementfurther includes glass.
 22. The system of claim 5 wherein said lasermedium element includes erbium.
 23. The system of claim 5 wherein saidlaser medium element includes thorium.
 24. The system of claim 5 whereinsaid laser medium element includes holmium.
 25. The system of claim 4wherein said output coupler is disposed at a second end of said opticalpath, for reflecting light of said first frequency back along saidoptical path and passing light of said second frequency as amplifierpump laser output pulses, thereby establishing an optical resonatorbetween said first reflector and said output coupler.
 26. The system ofclaim 25 wherein said diode laser is disposed to side pump said lasermedium element.
 27. The system of claim 25 wherein said diode laser isdisposed to end pump said laser medium element.
 28. The system of claim4 further including a second reflector disposed at a second end of saidoptical path for redirecting said beam back along said optical path, andwherein said output coupler redirects said light of said first frequencyalong said optical path between said first and second reflectors,thereby establishing an optical resonator between said first and secondreflectors.
 29. The system of claim 28 wherein said diode laser isdisposed to side pump said laser medium element.
 30. The system of claim28 wherein said diode laser is disposed to end pump said laser mediumelement.
 31. The system of claim 3 wherein said amplifier pump lasercomprises:a laser medium element for emitting a laser beam at a firstoptical frequency; a diode laser for emitting laser light to excite saidlaser medium element to emit said laser beam; a beam director fordirecting said beam along a looped optical path; a frequency alteringdevice interposed in said optical path for altering the frequency of aportion of said beam, from said first frequency to a second frequency;an output coupler for reflecting light of said first frequency alongsaid optical path and passing light of said second frequency asamplifier pump laser output; and a switching device, responsive to anexternal signal, for selectively frustrating or allowing opticalresonance.
 32. The system of claim 31 wherein said diode laser isdisposed to side pump said laser medium element.
 33. The system of claim31 wherein said diode laser is disposed to end pump said laser mediumelement.
 34. The system of claim 2 wherein said regenerative amplifieris ring configured.
 35. The system of claim 34 wherein said amplifierpumping laser comprises:a laser medium element for emitting a laser beamat a first optical frequency along an optical path passing through saidelement; a diode laser for emitting laser light to excite said lasermedium element to emit said laser beam; a first reflector disposed at afirst end of said optical path for redirecting said beam back along saidoptical path; a frequency altering device interposed in said opticalpath for altering the frequency of a portion of said beam from saidfirst frequency to a second frequency; an output coupler disposed toreflect light of said first frequency along said optical path and topass light of said second frequency as amplifier pump laser outputpulses; and a switching device disposed in said optical path andresponsive to an external signal, for selectively frustrating orallowing optical resonance.
 36. The system of claim 35 wherein saidoutput coupler is disposed at a second end of said optical path, forreflecting light of said first frequency back along said optical pathand passing light of said second frequency as amplifier pump laseroutput pulses, thereby establishing an optical resonator between saidfirst reflector and said output coupler.
 37. The system of claim 35further including a second reflector disposed at a second end of saidoptical path for redirecting said beam back along said optical path, andwherein said output coupler redirects said light of said first frequencyalong said optical path between said first and second reflectors,thereby establishing an optical resonator between said first and secondreflectors.
 38. The system of claim 34 wherein said amplifier pump lasercomprises:a laser medium element for emitting a laser beam at a firstoptical frequency; a diode laser for emitting laser light to excite saidlaser medium element to emit said laser beam; a beam director fordirecting said beam along a looped optical path; a frequency alteringdevice interposed in said optical path for altering the frequency of aportion of said beam, from said first frequency to a second frequency;an output coupler for reflecting light of said first frequency alongsaid optical path and passing light of said second frequency asamplifier pump laser output; and a switching device, responsive to anexternal signal, for selectively frustrating or allowing opticalresonance.
 39. The system of claim 1 wherein said amplifier is asingle-pass optical amplifier.
 40. The system of claim 1 wherein saidamplifier is a multi-pass optical amplifier.
 41. The system of claim 1wherein said amplifier pumping laser comprises:a laser medium elementfor emitting a laser beam at a first optical frequency along an opticalpath passing through said element; a diode laser for emitting laserlight to excite said laser medium element to emit said laser beam; afirst reflector disposed at a first end of said optical path forredirecting said beam back along said optical path; a frequency alteringdevice interposed in said optical path for altering the frequency of aportion of said beam from said first frequency to a second frequency; anoutput coupler disposed to reflect light of said first frequency alongsaid optical path and to pass light of said second frequency asamplifier pump laser output pulses; and a switching device disposed insaid optical path and responsive to an external signal, for selectivelyfrustrating or allowing optical resonance.
 42. The system of claim 41wherein said laser medium element is a cylindrical solid.
 43. The systemof claim 42 wherein said diode laser is disposed to side pump said lasermedium element.
 44. The system of claim 41 wherein said output coupleris disposed at a second end of said optical path, for reflecting lightof said first frequency back along said optical path and passing lightof said second frequency as amplifier pump laser output pulses, therebyestablishing an optical resonator between said first reflector and saidoutput coupler.
 45. The system of claim 44 wherein said laser mediumelement is a cylindrical solid.
 46. The system of claim 45 wherein saiddiode laser is disposed to side pump said laser medium element.
 47. Thesystem of claim 41 further including a second reflector disposed at asecond end of said optical path for redirecting said beam back alongsaid optical path, and wherein said output coupler redirects said lightof said first frequency along said optical path between said first andsecond reflectors, thereby establishing an optical resonator betweensaid first and second reflectors.
 48. The system of claim 47 whereinsaid laser medium element is a cylindrical solid.
 49. The system ofclaim 48 wherein said diode laser is disposed to side pump said lasermedium element.
 50. The system of claim 1 wherein said amplifier pumplaser comprises:a laser medium element for emitting a laser beam at afirst optical frequency; a diode laser for emitting laser light toexcite said laser medium element to emit said laser beam; a beamdirector for directing said beam along a looped optical path; afrequency altering device interposed in said optical path for alteringthe frequency of a portion of said beam, from said first frequency to asecond frequency; an output coupler for reflecting light of said firstfrequency along said optical path and passing light of said secondfrequency as amplifier pump laser output; and a switching device,responsive to an external signal, for selectively frustrating orallowing optical resonance.
 51. The system of claim 50 wherein saidlaser medium element is a cylindrical solid.
 52. The system of claim 51wherein said diode laser is disposed to side pump said laser mediumelement.